Resorufin β-D-galactopyranoside is a fluorogenic substrate for β-galactosidase.1 Upon enzymatic cleavage by β-galactosidase, the fluorescent moiety resorufin is released and its fluorescence can be used to quantify β-galactosidase activity. Resorufin displays excitation/emission maxima of 570/580 nm, respectively.
References
1. Hofmann, J., and Sernetz, M. Immobilized enzyme kinetics analyzed by flow-through microfluorimetry: Resorufin-β-D-galactopyranoside as a new fluorogenic substrate for β-galactosidase. Analytica Chimica Acta 163, 67-72 (1984).